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Stroke Incidence and Mortality Trends in US Communities, 1987 to 2011
Study Questions:
What are the trends in stroke incidence and subsequent mortality among black and white adults in the Atherosclerosis Risk in Communities (ARIC) cohort, from 1987 to 2011?
Methods:
This was a prospective cohort study of 14,357 participants (282,097 person-years) free of stroke at baseline, facilitated in four different US communities. Participants were recruited for the purpose of studying all stroke hospitalizations and deaths, and for collection of baseline information on cardiovascular risk factors (via interviews and physical examinations) in 1987-1989. Participants were followed up (via examinations, annual phone interviews, active surveillance of discharges from local hospitals, and linkage with the National Death Index) through December 31, 2011. The study physician reviewers adjudicated all possible strokes and classified them as definite or probable ischemic or hemorrhagic events. The main outcomes and measures were trends in rates of first-ever stroke per 10 years of calendar time estimated using Poisson regression incidence rate ratios (IRRs), with subsequent mortality analyzed using Cox proportional hazards regression models and hazard ratios (HRs) overall and by race, sex, and age divided at 65 years.
Results:
Among 1,051 (7%) participants with incident stroke, there were 929 with incident ischemic stroke and 140 with incident hemorrhagic stroke (18 participants had both during the study period). Crude incidence rates were 3.73 (95% confidence interval [CI], 3.51-3.96) per 1,000 person-years for total stroke, 3.29 (95% CI, 3.08-3.50) per 1,000 person-years for ischemic stroke, and 0.49 (95% CI, 0.41-0.57) per 1,000 person-years for hemorrhagic stroke. Stroke incidence decreased over time in white and black participants (age-adjusted IRRs per 10-year period, 0.76 [95% CI, 0.66-0.87]; absolute decrease of 0.93 per 1,000 person-years overall). The decrease in age-adjusted incidence was evident in participants ages 65 years and older (age-adjusted IRR per 10-year period, 0.69 [95% CI, 0.59-0.81]; absolute decrease of 1.35 per 1,000 person-years), but not evident in participants younger than 65 years (age-adjusted IRR per 10-year period, 0.97 [95% CI, 0.76-1.25]; absolute decrease of 0.09 per 1,000 person-years) (p = 0.02 for interaction). The decrease in incidence was similar by sex. Of participants with incident stroke, 614 (58%) died through 2011. The mortality rate was higher for hemorrhagic stroke (68%) than for ischemic stroke (57%). Overall, mortality after stroke decreased over time (hazard ratio [HR], 0.80 [95% CI, 0.66-0.98]; absolute decrease of 8.09 per 100 strokes after 10 years [per 10-year period]). The decrease in mortality was mostly accounted for by the decrease at younger than age 65 years (HR, 0.65 [95% CI, 0.46-0.93]; absolute decrease of 14.19 per 100 strokes after 10 years [per 10-year period]), but was similar across race and sex.
Conclusions:
The authors concluded that stroke incidence and mortality rates decreased from 1987 to 2011, with variation across age groups, but similar reductions across sex and race.
Perspective:
This study demonstrated a significant decrease in stroke incidence from 1987 to 2011 in white and black participants and in men and women. However, the decrease in stroke incidence was observed only at ages older than 65 years. Stroke mortality decreased as well. This decrease was generally similar in men and women and by race. In contrast to incidence trends, the biggest decrease in stroke mortality was found at a younger age. Thus, the overall decline in stroke mortality is a combination of different decreases in stroke incidence and mortality across age groups. Declines in stroke incidence likely reflect changes in lifetime risk factor levels, whereas improved survival may be attributed to time trends in medical care, in stroke severity, or both.
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